Thermoplastic polymers are utilized to prepare molded parts in a variety of industries, for example automotive, toys, appliances, farm and lawn tractors and implements, medical devices, food service items, electronic equipment components, and the like. Thermoplastic polymers provide significant advantages for molded products, for example lighter weight than some alternative materials, design flexibility, controlled conductivity, and the like. In some applications thermoplastic polymers present challenges, for example higher coefficient of liner expansion (CLTE), lower modulus, lower conductivity and higher brittleness than alternative materials. Fillers, such as fibers, can be added to improve CLTE, modulus and based on the nature and content of the fibers, conductivity. The backbone of thermoplastic polymers can be modified to add elastomeric nature or elastomeric polymers can be blended with base thermoplastic polymers to reduce the brittleness of molded parts derived from thermoplastic materials. Thermoplastic polymer systems containing styrenic polymers modified with elastomeric monomers or blended with elastomeric polymers are recognized as providing very good properties, such as heat stability, relatively high modulus and good modulus at elevated temperatures. Molded parts prepared from many thermoplastic polymer systems require relatively thick cross-sections (for example thick walls) to provide the strength and stiffness required for the desired application. One advantage of parts molded from thermoplastic systems is that surfaces of the molded products can be modified to match functional or aesthetic requirements, surface modified parts can be relatively glossy using some polymer systems and processing techniques. For some applications low gloss is desired. This can present an additional challenge to a parts manufacturer. Polymer systems based on styrenic polymers, especially those modified to add elastomeric properties, have improved stiffness, modulus and modulus at elevated temperatures thereby allowing the use of thinner cross-sections to reach the desired properties.
Thermoplastic polymers systems containing styrenic polymers have been modified with fibers as disclosed, in for example, WO 2011/023541; WO 2005/090451; U.S. Pat. Nos. 8,030,393 and 7,135,520 incorporated herein by reference in their entirety. Such systems have not achieved commercial success due to problems with pellet robustness, for example poor adhesion of the polymer matrix to the fibers, and poor flow properties making processing of such materials a challenge. Thus despite the desirable properties of styrenic polymer systems, fiber modified systems have not provided all of the desired properties and been processable.
Thus, what is needed is thermoplastic concentrates containing styrenic polymers and fibers which exhibit improved pellet robustness and flow properties, moldable compositions based on thermoplastic concentrates containing styrenic polymers and fibers having low water absorbtion, good retention of modulus at elevated temperatures. It is further desired that such moldable compositions facilitate the preparation of molded parts with thinner cross-sections required to meet use strength requirements and which provides low gloss on grained surfaces. What is needed is a concentrate of fibers in a thermoplastic polymer system containing styrenic polymers and moldable compositions derived therefrom having an improved balance of properties, such as high stiffness, good practical ductility, high heat performance and good processability. What are also needed are methods for preparing such concentrates, moldable compositions and molded parts derived therefrom which are commercially viable.